1. Technical Field
The present invention relates to a mobile communication system.
2. Background Art
FIG. 7 illustrates the bearer configuration and the protocol stack for sending a control signal between a mobile station UE and a mobile switching center MME in the LTE scheme (Release. 8) as defined by the 3GPP.
As illustrated in FIG. 7, as bearers for the C-plane, a signaling radio bearer (SRB; RRC connection) is provided between the mobile station UE and the radio base station eNB, and a wired bearer (S1 connection) is provided between the radio base station eNB and the mobile switching center MME.
As radio bearer functions of setting the radio bearer with the radio base station eNB, the mobile station UE further includes a physical (PHY) layer function, an MAC (Media Access Control) layer function, an RLC (Radio Link Control) layer function, a PDCP (Packet Data Convergence Protocol) layer function, and an RRC (Radio Resource Control) layer function.
As radio bearer functions of setting the radio bearer with the mobile station UE, the radio base station eNB also includes a physical (PHY) layer function, an MAC layer function, an RLC layer function, a PDCP layer function, and an RRC layer function.
Further, as wired bearer functions of setting the wired bearer with the mobile switching center MME, the radio base station eNB includes a network layer 1 (NW L1) function, a network layer 2 (NW L2) function, an IP (Internet Protocol) layer function, an SCTP (Stream Control Transmission Protocol) layer function, and an S1AP layer function.
Similar, as wired bearer functions of setting the wired bearer with the radio base station eNB, the mobile switching center MME includes a network layer 1 (NW L1) function, a network layer 2 (NW L2) function, an IP layer function, an SCTP layer function, and an S1AP layer function.
As illustrated in FIG. 7, the control signals (NAS (Non Access Stratum) signals and S1AP signals) are configured to be sent and received between the mobile station UE and the mobile switching center MME on the radio bearers and wired bearers described above.
In a mobile communication system of the LTE-Advanced scheme, which is the communication scheme that is the next-generation of the LTE scheme, a connection to “relay nodes RN” can be established between the mobile station UE and the radio base station eNB.
However, the conventional mobile communication system has been problematic in that, when the relay nodes RN are employed, the bearer configuration and protocol stack for sending the control signals mentioned above cannot be applied, because there is no intention for the mobile station UE to send and receive control signals with the mobile switching center MME via a plurality of devices provided with the functions of the radio base station eNB.